How could it not be possible. In ancient times, this was common sense. Each country, sometimes each city, had its own pantheon of gods. We Olympians have always been used to living in close proximity to, ah...the competition.

Mythology is a collection of myths, especially one belonging to a particular religious or cultural tradition of a group of people – their collection of stories they tell to explain nature, history, and customs – or the study of such myths.[1]

Roman mythology

Roman mythology is the collection of myths belonging to the ancient Romans. It is prominently featured in The Heroes of Olympus series. When the flame of Western Civilization shifted from Greece to Rome, many of the Greek myths were reinterpreted under Roman names, thus causing the gods to develop alternate forms and forming the basis of Roman mythology.